This invention concerns improvements in or relating to car head-up displays and more particularly to projection units for such displays.
There have been numerous proposals for car head-up display systems of varying complexity and practicality. Many proposals have employed projection optics with refractive lenses and/or diffractive elements to give high image quality but these can tend to make the system bulky or expensive. Also systems which give excellent imagery for one particular design position can sometimes suffer rapid deterioration on departure from that design position, particularly when off-axis optics are involved. European Patent Application EP 0 391 231A discloses a particular example having an off-axis aspheric mirror which is tiltably adjustable.